Scaphoid (PA axial view)
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This view aims to show the scaphoid in its true anatomical appearance without any superimposition or foreshortening. As the scaphoid sits in a slight volar tilt, the angle of the axial view ensures there is no superimposition hence allowing the visualization of any subtle distal, middle or proximal fractures 1 of the scaphoid.
- patient is seated alongside the table
- the affected arm if possible is flexed at 90° so the arm and wrist can rest on the table
- the affected hand is placed, palm down on the image receptor with hand in ulnar deviation (see practical points)
- shoulder, elbow, and wrist should all be in the transverse plane, perpendicular to the central beam
- the wrist and elbow should be at shoulder height which makes radius and ulna parallel (lowering the arm makes radius cross the ulna and thus relative shortening of radius)
- posteroanterior axial projection
- anatomical snuffbox
- the central beam is angled 15-30° proximally along the long axis of the arm towards the elbow
- laterally to the skin margins
- distal to the base of the first metacarpal
- proximal to the radiocarpal joint
- 18 cm x 24 cm
- 55-65 kVp
- 3-5 mAs
- 100 cm
Image technical evaluation
- the scaphoid should appear slightly elongated and almost free from all superimposition
- minor superimposition of the metacarpal bases
- articulation between the distal radius and the ulna is open or has little superimposition.
The scaphoid does not sit 100% flush with the image receptor when the hand is resting (see Figure 1), the scaphoid has a natural palmar tilt, therefore angling to that tilt will result in a 'truer' PA radiograph.
It is important to remember why you are angling the central ray. Some patients will have little tolerance to the ulnar deviation, and too much angle will only distort the scaphoid via superimposition. More often than not, if the scaphoid is profoundly elongated with overlaying anatomy, you have angled too much.
Ulnar deviation is necessary as it moves the scaphoid away from the radius and rotates it in the palmer aspect, minimizing superimposition and achieving a pure PA projection 1-3. However, patients with a fractured scaphoid will be in a lot of pain so deviating their hand to the ulna can be quite a task; only deviate the hand as much as the patient can bear it.
More often than not, the pain has not been addressed yet. Offer to move things around to assist in positioning - simple things like lowering/raising the table can go a long way and result in a better experience for the patient. It is important to remember this when examining your patient, as it is easy to forget that only lifting your hand up and placing it on an image receptor could result in substantial pain.